The present invention relates to a jointing apparatus for jointing thermo plastic pipes by using frictional heat caused by vibration.
Recently, polyethylene pipe, which is a thermo plastic pipe, is coming to be used commonly for gas piping or water piping. Because, the polyethylene pipe is excellent not only in corrosion resistance, but also in earthquake resistance due to its large extensibility. In such a situation, a method for jointing thermo plastic pipes more effectively and securely and an apparatus for this method are demanded increasingly.
As a conventional method for jointing polyethylene pipes, a butt welding method using a flat-plate-shaped hot plate, a socket welding method using a socket, or the like is used. The butt welding method consists in heating respective extremities of pipes to be jointed by means of a hot plate heated to a high temperature having a larger cross-section than the pipe diameter, thereafter removing the hot plate, butting end faces of the pipes to be jointed and welding under pressure. As representative methods of the socket welding method, there are a method for welding similarly to said butt fusion method using a hot plate having a shape that corresponds with a shape of a used socket and a method for welding by using a socket having an implanted electric heating element wire such as Nichrome wire and supplying this electric heating element wire with electricity to heat the external surface of the pipe and the internal surface of the socket and thereby weld them.
Besides, jointing methods for butting and jointing plastic pipes, by using frictional heat generated on butting junction faces of plastic pipes by turning the pipes in reverse directions to each other, in place of using a hot plate or an electric heating element as mentioned above, are disclosed in Japanese Patent Publications No. Hei 2-13619, No. Shou 63-39415 and others. The art disclosed in the Japanese Patent Publication No. Hei 2-13619 is to obtain a connecting joint without requiring burring, by using friction caused by rotation. In Japanese Patent Publication No. Shou 63-39415, a terminal portion of a socket is pressed to the front end of a plastic pipe to obtain friction caused by rotation so that the shape of the terminal portion of the socket may be independent of the diameter of the plastic pipe and easier molding of the socket can be expected.
On the other hand, Japanese Patent Laid-Open No. Shou 62-35830 proposes a method for manufacturing a support with a cap. This method is to weld the outer circumference of a support body and a cap only at required points without using a specific heating device, by introducing an extremity of the support body into a cavity of the cap made of synthetic resin mold, and turning the outer circumference of the support body relatively to the cap. Japanese Patent Laid-Open No. Shou 62-248236 describes a jointing method of thermo plastic pipes of different diameter by frictional heat. Besides, Japanese Patent Laid-Open No. Hei 02-248236(Japanese Patent Publication No. Hei 5-36225) also proposes a jointing method using frictional heat between plastic materials.
Moreover, the Inventors have already proposed a basic method for jointing plastic pipes by applying rectilinear vibration to generate frictional heat and applied for a patent by filing Japanese Patent Applications No. Hei 7-196625, No. Hei 7-240522 and No. Hei 8-68989.
In a butt welding method or a socket welding method using a hot plate mentioned above, as a hot plate is used repeatedly, soil deposited on the hot plate sticks to the pipe end face so that junction surfaces come to include impurities resulting in junction defects.
Moreover, with the electric heating of a hot plate, it takes long time about 700 sec from the beginning of electric supply to the plate to the completion of welding, resulting in low labor effectiveness. When a socket having an electric heat element wire such as Nichrome wire implanted therein is used, it is necessary to provide a socket including a heat element wire every time a couple of pipes are to be jointed and a great number of sockets should be prepared provoking some questions from economical point of view. Further, since it takes about 1700 sec from the beginning of electric supply to the completion of welding, a labor effectiveness problem is caused especially when a number of pipes are to be jointed.
In the case of the butt jointing of pipes by using heat generated by rotational friction as described, for example, in Japanese Patent Publication No. Hei 02-13619, a large amount of energy is necessary for rotating the entire pipes to be jointed.
What is described in Japanese Patent Laid-Open No. Shou 62-35830 is not for a butt jointing of both polyethylene pipes but of entirely different pipes; so it is difficult to apply this method to butt jointing of both polyethylene pipes. Because, in the method described in said document, the junction strength is ensured by inserting a mandrel into a cavity in a way to increase contact area in order to enlarge the junction surface, while such enlarged junction surface is not allowed in butt jointing.
On the other hand, when polyethylene pipes of an identical diameter are to be jointed, the contact area is small so that the method described in Japanese Patent Laid-Open No. Shou 62-248623 can not ensure a sufficient reliability, because of low mechanical strength per unit area obtained by the method. As a result, in practice, the jointing strength is increased by increasing the contact area through the use of pipes having different diameters.
The invention of Japanese Patent Laid-Open No. Hei 02-248236 (Japanese Patent Publication No. Hei 5-36225) is an example of friction jointing of solid rods using mechanical rotation; however it is also difficult to ensure junction strength for the jointing of pipes (hollow cylinder), having small junction cross section, causing a reliability problem.
On the other hand, vibration jointing methods and apparatus of Japanese Patent Applications No. Hei 7-196625, No. Hei 7-240522 and No. Hei 8-68989 already filed by the Inventors are to verify a laboratory level principle and are not practical enough to be applied on jobsites. Besides, a method for generating frictional heat by orbital movement of pipe end faces, by using electromagnets (or permanent magnets), is proposed in Japanese Patent Application No. Hei 7-196625, but the adoption of electromagnets complicated the apparatus itself excessively.
In other words, conventional apparatus have not be well devised from structural point of view, as a vibration jointing apparatus appropriated to be used in the practical field, such as a piping jobsite for gas, water or the like.